1. Field of the Invention
The present invention relates to LCD displays. Specifically, the invention relates to using a single inverter to drive multiple lamps in an LCD panel backlight.
2. Description of the Related Art
Liquid Crystal Displays (LCD) utilize liquid crystal molecules to form pixels of a display. Electrical charges on a liquid crystal cause it to align in a helical structure. The amount of electricity required is low and the technology is commonly utilized in display panels because of the low energy requirement and compact size.
The liquid crystals are not self-illuminating and light must be projected onto them from an external light source. The LCD then acts to polarize light and uses polarization to “shutter” light to create dark images and to allow light to pass through for bright objects. In color LCDs, the polarization is used similarly on multiple red, green and blue pixels to create any one of millions of colors. The common light source for a display panel is a backlight. The backlight consumes much more energy then the LCD and is typically a series of lamps mounted on the LCD's back panel. These lamps are typically cold cathode fluorescent lamps (CCFL).
Conventional circuit designs for LCD backlight displays use a low power direct current (DC) power supply to power the lamp or lamps that illuminate the LCD. The current from the low power DC power supply is converted to higher voltage alternating current (AC). The industry standard specification of the lamps used in LCD panel backlights require high voltages to start up the lamps and keep the lamps on. As a result, despite being converted to high voltage AC, the higher voltage may be only sufficient to power a single lamp. That means each lamp in a group of lamps (typically more than one is required in most modern LCD panels) must have its own inverter associated with it.
The backlight unit constitutes a significant portion of the overall manufacturing cost of an LCD panel display. Part of the high manufacturing cost of the backlight units is due to the fact that each lamp requires its own inverter. With small panel displays, manufacturing costs are not as affected by the requirement that each lamp have its own inverter because of the relatively low number of lamps and associated inverters required. However, with large panel displays that require 20-40 lamps, the requirement that each lamp have its own inverter constitutes a large portion of the backlight's manufacturing cost.
Other consequences of having a large number of inverters in the backlight includes: decreased energy efficiency, decreased reliability and variations in illumination uniformity.
Therefore, there is a need for a way to power multiple lamps from a single inverter. Such a device would drastically lower the number of inverters required, which will make the manufacture of large screen LCD panels substantially more cost effective. Also, with fewer total inverters in the overall system, energy efficiency is increased, reliability is increased and illumination uniformity is easier to control.